Large enterprises, using directories with virtual attributes (attributes whose values do not reside in the directory), need a way to federate virtual attributes across directories in different domains in a manner in which they can provide consistent results in any environment. Federation of virtual attributes poses unique challenges due to the dynamic nature of the virtual attribute. Unlike normal attributes, the virtual attribute does not have a physical value that can be propagated. Also, the virtual value may change rapidly. Propagating the virtual value through traditional directory integration causes problems because by the time the values are propagated they may already be stale or out of date.
Just In Time (JIT) directory integration provides an option, but every level of indirection adds latency, processor load, and bandwidth load. Database federation would not work because the operating environments (e.g., directory structure, external ports) differ for different directories and would cause problems for the calculation method.